SN3 SHORT NOTE 5M ★ High-yield

Describe the principles of prescribing in the elderly and in children.

Pharmacology · 2nd Professional — Para-Clinical

WHY the Elderly Are Different

Change	Consequence	Example
Reduced glomerular filtration	The single most important change — renally excreted drugs accumulate. Creatinine may look normal because muscle mass is reduced, so it overestimates renal function in the elderly	Digoxin, aminoglycosides, metformin, lithium, DOACs
Reduced hepatic mass and blood flow	Reduced first-pass metabolism and clearance	Propranolol, morphine, benzodiazepines
Increased body fat, reduced body water	Larger volume of distribution and longer half-life for lipid-soluble drugs	Diazepam — markedly prolonged
Reduced albumin	More free drug for highly bound agents	Warfarin, phenytoin
Increased CNS sensitivity and a more permeable barrier	Greater effect at the same concentration	Benzodiazepines, opioids, antimuscarinics — confusion and falls
Impaired homeostatic reflexes	Baroreceptor and thermoregulatory responses blunted	Postural hypotension and falls with antihypertensives
Multiple comorbidity and polypharmacy	Interactions, adherence problems, prescribing cascades	—

CLINICAL PEARL

A normal serum creatinine in an 80-year-old does not mean normal renal function. Creatinine comes from muscle, and an elderly person has much less of it, so the same clearance produces a lower number. Estimated GFR or a Cockcroft–Gault calculation using age and weight is what should guide dosing — and failing to do this is among the commonest causes of drug toxicity in older patients.

Drugs to Avoid or Use Cautiously in the Elderly

Long-acting benzodiazepines — falls, hip fracture, confusion
Antimuscarinics of every kind — first-generation antihistamines, tricyclics, oxybutynin, older antipsychotics; the cumulative "anticholinergic burden" causes confusion, retention, constipation and falls
NSAIDs — gastrointestinal bleeding, renal failure, heart failure, hypertension
Antipsychotics in dementia — increased stroke and mortality
Digoxin at higher doses, sulphonylureas with a long action (glibenclamide), and drugs causing postural hypotension
Explicit criteria exist — the Beers criteria and STOPP/start tools list drugs to avoid and treatments wrongly omitted
"start low, GO slow" — begin at a reduced dose and titrate against response

Prescribing for Children

Children are not small adults — absorption, distribution, metabolism and excretion all differ, and differ again between the neonate, infant and older child
Neonates — immature hepatic glucuronidation (chloramphenicol causes grey baby syndrome), immature renal function, a permeable blood–brain barrier, lower albumin with fetal albumin binding poorly, and greater total body water
Kernicterus — sulphonamides, ceftriaxone and diazepam displace bilirubin from albumin in the jaundiced neonate
Dosing is by body weight or surface area, never by fraction of an adult dose; and older children may need proportionally higher doses per kilogram because metabolism is faster
Drugs to avoid in children — aspirin (Reye syndrome), tetracyclines under 8 (teeth), fluoroquinolones (arthropathy, though used where the benefit is clear), codeine (fatal respiratory depression in ultra-rapid metabolisers), and chloramphenicol in neonates
Formulation matters — palatable liquids, dispersible tablets, and a device that measures accurately; a teaspoon is not a measure

Applied Aspects

Estimate renal function before prescribing to any elderly patient, and reassess during acute illness when it falls further
Review the whole drug list at every visit, ask what is actually being taken, and stop what is no longer needed; the single most valuable intervention in geriatric prescribing
Consider an adverse effect first when an older patient develops confusion, falls, incontinence or immobility; these are commonly iatrogenic and reversible
Check that the patient can open the container, read the label and remember the schedule; blister packs, large print and a dosette box change adherence more than any explanation
Weigh every child before prescribing, and calculate rather than estimate; tenfold dosing errors in paediatrics are a documented and recurring cause of death
Many drugs are used off-label in children because trials exclude them; this is often necessary but should be recognised, and paediatric formularies consulted

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